U.S. patent application number 10/580937 was filed with the patent office on 2007-05-24 for thickener for paper coating compositions.
Invention is credited to Detlev Glittenberg.
Application Number | 20070113997 10/580937 |
Document ID | / |
Family ID | 34626439 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070113997 |
Kind Code |
A1 |
Glittenberg; Detlev |
May 24, 2007 |
Thickener for paper coating compositions
Abstract
A paper coating composition comprising one or more thickeners,
characterised in that at least one of said one or more thickeners
is a cold water swellable starch ester, methods of preparing such
compositions and their use in coating paper products.
Inventors: |
Glittenberg; Detlev;
(Krefeld, DE) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
PO BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
34626439 |
Appl. No.: |
10/580937 |
Filed: |
November 26, 2004 |
PCT Filed: |
November 26, 2004 |
PCT NO: |
PCT/EP04/13433 |
371 Date: |
May 30, 2006 |
Current U.S.
Class: |
162/175 ;
106/207.1 |
Current CPC
Class: |
D21H 19/54 20130101 |
Class at
Publication: |
162/175 ;
106/207.1 |
International
Class: |
C09J 103/06 20060101
C09J103/06; D21H 17/00 20060101 D21H017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2003 |
EP |
03257477.4 |
Claims
1. A paper coating composition comprising one or more thickeners,
characterised in that at least one of said one or more thickeners
is a cold water swellable starch ester.
2. A paper coating composition according to claim 1, characterised
in that the starch ester is a starch carbamate phosphate ester.
3. A paper coating composition according to claim 1, characterised
in that the starch ester is derived from potato or tapioca
starch.
4. A paper coating composition according to claim 1, characterised
in that it comprises 0.005-2% by dry weight of said starch
ester.
5. A paper coating composition according to claim 1, characterised
in that the composition further comprises one or more pigments, one
or more binders and, optionally, one or more additives.
6. A paper coating composition according to claim 1, characterised
in that the composition comprises 30-75% by weight dry
substance.
7. (canceled)
8. A process for the preparation of a paper coating composition
comprising adding one or more pigments, one or more thickeners, one
or more binders and, optionally, one or more additives to an
aqueous solution and mixing the solution, characterised in that at
least one of said one or more thickeners is a cold water swellable
starch ester.
9. A process according to claim 8 characterised in that the one or
more binders are added to the aqueous solution before the one or
more thickeners.
10. A process according to of claim 8 characterised in that, for
100 parts pigment, the composition comprises 0.01-2 parts starch
ester.
11. A method of manufacturing paper comprising applying to at least
one surface of a sheet of paper or a paper web a composition
according to claim 1 or prepared according to the process of claim
8.
12. A method according to claim 11, further comprising the steps of
removing any excess coating composition, drying and, optionally,
calendering the sheet of paper or paper web.
13. A paper product coated with a composition according to claim 1
or manufactured according to the method of claim 11.
14. A paper coating composition according to claim 1, characterised
in that it comprises 0.008-1.7% by dry weight of said starch ester.
Description
TECHNICAL FIELD
[0001] The present invention relates to paper coating compositions
comprising a starch-based thickener, to paper products coated with
such compositions and to methods of preparing such compositions and
products.
BACKGROUND OF THE INVENTION
[0002] Coating compositions have been developed that can
contribute, amongst other things, to improved appearance and feel
(e.g. improved gloss, slickness, brilliance, and colour), improved
printability (e.g. smear-resistance, ink-absorption and adhesion)
and improved strength. The ingredients included in such
compositions can be divided into three main categories: pigments,
binders and thickeners.
[0003] Thickeners, in particular, have to be chosen very carefully
as they are responsible for determining the coating composition's
Theological properties. It will have to be ensured, for example,
that at low shear the coating composition has a low enough
viscosity for easy pumping but a high enough viscosity to maintain
a homogeneous suspension and to prevent excessive absorption into
the paper. At high shear (for example during blade application of
the composition), the viscosity will have to be low enough to
ensure that an even coating of the composition can be applied over
the entire surface of the paper without having to apply too high a
blade pressure to obtain the desired coat weight. In addition, the
coating composition should have good water retention values and
torque properties and should be stable during storage and at the
high temperatures required for drying. To meet all of these
requirements, a number of different thickeners have been
proposed.
[0004] To date, the most commonly used thickeners have included
cellulose ethers such as carboxymethyl cellulose (CMC), modified
starches and synthetic products such as water-soluble polymers.
Unfortunately, none of these products have proved to be entirely
satisfactory.
[0005] Cellulose ethers suitable for use as thickeners tend to be
obtainable only by relatively complex preparation methods. This is
a disincentive in itself but also means that such products carry a
prohibitively high price tag. What is more, it has often been found
that cellulose ether-based compositions do not have good stability
(in terms of viscosity) at high shear or at high temperature.
Although some synthetic polymers have been developed to replace
cellulose ethers, these do not tend to have comparable thickening
properties, for example in terms of water retention.
[0006] Similarly, although some starch thickeners have been
suggested (including, in particular, cold water soluble starches
obtained e.g. by roll drying of native or chemically modified
starches), these do not provide the necessary viscosity to the
coating compositions at typical thickener addition levels, i.e.
generally less than 2 parts per 100 parts pigment. Higher addition
levels of such starches become uneconomic and furthermore can
impair desired properties of the final coated papers such as e.g.
gloss and mottling. Furthermore, at higher addition levels, the
starches would be referred to as co-binders rather than
thickeners.
[0007] It is therefore apparent that there is a need in the art for
coating compositions comprising improved thickeners. The present
invention provides such compositions.
SUMMARY OF THE INVENTION
[0008] In a first aspect of the present invention, there is
provided a paper coating composition comprising one or more
thickeners, characterised in that at least one of said one or more
thickeners is a cold water swellable starch ester. Preferably, at
least one of said one or more thickeners will be a starch carbamate
phosphate ester derived, for example, from potato or tapioca
starch.
[0009] According to one embodiment, the composition will further
comprise one or more pigments, one or more binders and, optionally,
one or more additives. It can be provided in dry or wet form. In
its wet form, it should comprise 30-75% by weight dry
substance.
[0010] According to a further aspect of the present invention,
there is provided the use of a cold water swellable starch ester as
a thickener in the preparation of a paper coating composition.
[0011] According to another aspect of the invention, there is
provided a process for the preparation of a paper coating
composition comprising adding one or more pigments, one or more
thickeners, one or more binders and, optionally, one or more
additives to an aqueous solution and mixing, characterised in that
at least one of said one or more thickeners is a cold water
swellable starch ester. Preferably, the one or more binders are
added to the aqueous solution before the one or more
thickeners.
[0012] According to yet another aspect of the present invention,
there is provided a method of manufacturing paper comprising
applying to at least one surface of a sheet of paper or a paper web
a composition as defmed above or prepared according to the process
described above. In one embodiment, the method will further
comprise the steps of removing any excess coating composition,
drying and, optionally, calendering the sheet of paper or paper
web.
[0013] According to a yet further aspect of the present invention,
there is provided a paper product coated with the above composition
or manufactured according to the above method.
DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a graphic representation of the Brookfield
viscosity of a reference coating composition and of coating
compositions comprising 0.2 parts CMC, 0.4 parts CMC, 0.6 parts
CMC, 0.06 parts Noresin.TM. (a cold water swellable starch ester),
0.25 parts Noresin.TM. and 0.35 parts Noresin.TM. respectively.
[0015] FIG. 2 is a graphic representation of the Haake viscosity of
the above listed compositions.
[0016] FIG. 3 is a graphic representation of the water retention
values of the above listed compositions.
[0017] FIG. 4 represents a comparison of the influence of CMC and
Noresin.TM. amounts on Brookfield viscosity.
[0018] FIG. 5 represents a comparison of the influence of CMC and
Noresin.TM. amounts on Haake viscosity.
[0019] FIG. 6 represents a comparison of the influence of CMC and
Noresin.TM. amounts on water retention values.
[0020] FIG. 7 is a graphic representation of the Brookfield
viscosity of compositions comprising the compositions produced in
Example 2.
[0021] FIG. 8 compares the Brookfield viscosity of fresh and stored
compositions.
[0022] FIG. 9 compares the Brookfield viscosity of fresh and stored
compositions.
[0023] FIG. 10 compares water retention values of fresh and stored
compositions.
[0024] FIG. 11 shows the influence of stirring time on Brookfield
viscosity.
[0025] FIG. 12 shows the influence of thickener type on torque.
[0026] FIG. 13 shows the influence of thickener dry solids content
on Brookfield viscosity.
DETAILED DESCRIPTION
[0027] The present invention provides a paper coating composition
comprising one or more thickeners, characterised in that at least
one of said one or more thickeners is a cold water swellable starch
ester. A cold water swellable (or "cold water swelling") starch
ester is a starch ester, substantially all of the granules of which
swell in cold water to give a viscous, colloidal dispersion. A
swollen starch granule is one whose size (observable e.g. by
microscopy) has at least doubled through absorption of water. Cold
water will be understood to be water having a temperature of less
than 50.degree. C., preferably between 5 and 40.degree. C., more
preferably between 10 and 35.degree. C., even more preferably
between 15 and 35.degree. C.
[0028] In a preferred embodiment of the present invention, the cold
water swellable starch ester will be a starch carbamate phosphate
ester. It can be derived from any type of starch including, for
example, potato, maize, wheat, rice, tapioca, sorghum and sago.
Preferably, however, it will be derived from potato or tapioca
starch.
[0029] According to one embodiment of the present invention, the
starch ester will be prepared by heating a mix of starch, acid,
urea, salt and water at low pressure. As noted above, the starch
will preferably be potato or tapioca derived starch. The acid will
ideally be a mineral acid such as phosphoric or sulphuric acid and
the salt will ideally be an alkaline salt such as an ammonium salt
or soda. For 100 parts starch, the initial mix should contain
0.02-100 parts each of acid, urea, salt and water. Preferably, for
100 parts starch, the mix will contain 2.5-40 parts of both acid
and urea and 0.05-40 parts of both salt and water. Ideally, for 100
parts starch, the mix should contain approximately 10 parts of both
acid and urea and approximately 5 parts of both salt and water. The
mix should be heated for up to 24 hours at a temperature of
80-220.degree. C. For best results, the mix should be heated for
2-5 hours at 120-160.degree. C. The heating should preferably be
carried out at a pressure between 0.001 and 0.8 bar. More
preferably, it should be carried out at a pressure between 0.1 and
0.2 bar. Starch esters prepared in this way have been found to
impart surprisingly good viscosity profiles when used as thickeners
in paper coating compositions.
[0030] In particular, it has surprisingly been found that coating
compositions comprising even only small amounts of such thickeners
have high (low shear) Brookfield viscosities (e.g. 400-2000 mpas)
and low high shear) Haake viscosities (e.g. 10-25 mPas). What is
more, unlike with conventional thickeners, the viscosities of these
compositions are very stable, even after overnight storage.
[0031] Thus, according to a preferred embodiment, cold water
swellable starch esters will be the only thickeners used in the
coating compositions of the present invention. Nonetheless, if
desired, one or more other thickeners may also be used. Preferably,
they will be selected amongst cold water soluble and/or cold water
swellable compounds including, but are not limited to, cellulose
ethers (such as CMC, hydroxyethyl cellulose, hydroxypropyl
cellulose, ethylhydroxyethyl cellulose and methyl cellulose),
alginates (such as sodium alginate), xanthan, carrageenans,
galactomannans (such as guar), native or modified starches (such as
roll-dried starch) and synthetic polymers (such as
polyacrylates).
[0032] In any event, the one or more cold water swellable starch
esters of the present invention should account for at least 50% of
total thickener content on a dry weight basis and for 0.005-2%,
preferably 0.008-1.7%, even more preferably 0.01-1.5% of the dry
weight of the overall coating composition. It has indeed been found
that, compared to conventional thickeners, much smaller amounts of
cold water swellable starch ester are needed to achieve the
necessary rheological properties for a good coating composition. As
a result, the coating compositions of the present invention will be
considerably cheaper to produce than more conventional ones.
[0033] The coating compositions of the present invention should, of
course, further comprise one or more pigments, one or more binders
and, optionally, one or more additives. The pigments, binders and
optional additive compounds can be selected amongst those available
in the art and in accordance with the type of coating composition
to be obtained.
[0034] Examples of pigments, both natural and synthetic, include:
clays such as structured and calcined clays, hydrated
aluminosilicates (such as kaolin clay), natural and synthetic
calcium carbonate, calcium sulphate, silicas, precipitated silicas,
titanium dioxide, alumina, aluminium trihydrate, plastic
(polystyrene) pigments, satin white, talc, barium sulphate and zinc
oxide. Preferably, the coating composition according to the present
invention will comprise pigment in an amount of approximately 30 to
99%, preferably 45 to 96% by weight of the dry solids.
[0035] Examples of binders suitable for use in the composition of
the present invention include: carbohydrate-based binders including
starch-based binders (such as oxidised or esterified starch) and
cellulose binders (such as CMC and hydroxyethyl cellulose), protein
binders (such as casein, gelatine, soy protein and animal glues)
and synthetic binders, especially latex binders (such as copolymer
latexes, acrylic polymer latexes, vinyl polymer latexes) and
synthetic resin binders. Preferably, the binder will selected such
that it is different from any of the one or more thickeners being
used and will be added to the coating composition in an amount of
0.5-50%, more preferably 1-35% by dry weight.
[0036] Of course, the choice of pigment and/or binder and the
amounts to be used will be determined in accordance with the
desired properties of the coating composition being produced.
[0037] The properties of the final coating composition can be
further modified or enhanced by the use of optional additives.
Examples of such additives include: surfactants (e.g. cationic
surfactants, anionic surfactants, non-ionic surfactants, amphoteric
surfactants and fluorinated surfactants), hardeners (e.g. active
halogen compounds, vinylsulfone compounds, epoxy compounds, etc.),
dispersing agents (e.g. polyacrylates, polyphosphates,
polycarboxylates, etc.), flowability improvers, lubricants (e.g.
calcium, ammonium and zinc stearate, wax or wax emulsions, alkyl
ketene dimer, glycols, etc.), antifoamers (e.g. octyl alcohol,
silicone-based antifoamers, etc.), releasing agents, foaming
agents, penetrants, optical brighteners (e.g. fluorescent
whiteners), preservatives (e.g. benzisothiazolone and isothiazolone
compounds), biocides (e.g. metaborate, thiocyanate, sodium
benzonate, etc.), yellowing inhibitors (e.g. sodium hydroxymethyl
sulfonate, sodium p-toluenesulfonate, etc.), ultraviolet absorbers
(e.g. benzotriazole compounds having a hydroxy-dialkylphenyl group
at the 2 position), antioxidants (e.g. sterically hindered phenol
compounds), insolubilisers, antistatic agents, pH regulators (e.g.
sodium hydroxide, sulfuric acid, hydrochloric acid, etc.),
water-resisting agents (e.g. ketone resin, anionic latex, glyoxal,
etc.), wet and/or dry strengthening agents (e.g. glyoxal based
resins, oxidised polyethylenes, melamine resins, urea formaldehyde,
etc.) gloss-ink holdout additives, grease and oil resistance
additives, leveling and evening aids (e.g. polyethylene emulsions,
alcohol/ethylene oxide, etc.), etc.
[0038] The amount of each of these compounds to be added, if at
all, will be determined in accordance with standard practice and
with the desired properties of the coating composition to be
produced in mind. The composition can be provided in dry form or in
an aqueous solution. The aqueous solution should have a total
content of 30-75% by weight dry substance. The remaining 25-70%
will consist essentially of water and/or other suitable fluids such
as solvents. If used, solvents will preferably be selected amongst
hydrophilic organic solvents such as methanol. Ideally however,
water alone will be used.
[0039] The paper coating composition in accordance with the present
invention can be prepared simply by mixing the above ingredients
(namely one or more pigments, one or more thickeners (at least one
of which is a cold water swellable starch ester), one or more
binders and, optionally, one or more additives) into the aqueous
solution. Thus, the present invention further provides a process
for the preparation of a paper coating composition and the use of a
cold water swellable starch ester in such a process.
[0040] As pigments are generally the ingredient present in the
largest amount, amounts of all other ingredients to be mixed into
the aqueous solution can conveniently be expressed as parts per 100
parts pigment. Thus, for 100 parts pigment, 0.01-2, preferably
0.1-1 parts cold water swellable starch ester and 1 to 50,
preferably 5 to 25 parts binder will be added to the aqueous
solution. The ingredients can be mixed in any order or
simultaneously. The cold water swellable starch ester can also be
dissolved separately in water (preferably at 1-10% dry substance,
more preferably at about 5% dry substance) and added to the
composition as a viscous solution. For more moderate thickening,
the one or more cold water swellable starch esters (whether
pre-dissolved or not) can be added to the composition after the one
or more binders. The ingredients should be mixed for a sufficient
time to form a substantially homogeneous slurry.
[0041] The coating composition thus prepared can either be stored
or it can be applied directly to paper. Thus, the present invention
further provides a method of manufacturing paper products
comprising applying to at least one surface of a sheet of paper or
paper web a composition as defined herein.
[0042] The terms "paper" and "paper product" refer to sheet
material of any thickness, including, for example, paper board,
cardboard and corrugated board. The term "paper web", by contrast,
refers to the continuous ribbon of paper, in its full width, at any
stage during the paper making process.
[0043] Coating of the paper products can be carried out on the
sheet forming machine or on a separate coating machine. Methods of
applying coating compositions to paper products are well known in
the art. They include, for example, air knife coating, rod coating,
bar coating, wire bar coating, spray coating, brush coating, cast
coating, flexible blade coating, gravure coating, jet applicator
coating, extrusion coating, short dwell coating, slide hopper
coating, curtain coating, flexographic coating, size-press coating,
gate roll coating, reverse roll coating and transfer roll coating.
According to the quality of paper desired, it can be coated only
once or a plurality of times, provided that at least one of the
coatings is in accordance with the present invention. If more than
one coating is to be applied, both surfaces of the paper web can be
coated.
[0044] After the coating step, excess coating composition can be
removed. The paper is then dried and optionally calendered to
improve surface smoothness and gloss and to reduce bulk. Drying
methods include, but are not limited to, air or convection drying
(e.g. linear tunnel drying, arc drying, air-loop drying, sine curve
air float drying, etc.), contact or conduction drying and radiant
energy drying (e.g. infrared or microwave drying). Calendering is
achieved by passing the coated paper between calender nips or
rollers (preferably elastomer coated nips or rollers) one or more
times. For best results, calendering should be carried out at
elevated temperatures. Ideally for each coating step, a dry coating
weight in the range from about 4 to about 30 g/M.sup.2, preferably
from about 6 to about 20 g/m.sup.2 will be achieved, with a coating
thickness of 1-50 .mu.m.
[0045] Advantageously, it has been found that use of the coating
composition of the present invention leads to smoother, higher
gloss paper products with improved optical properties such as
opacity and whiteness and improved printing properties such as
printing gloss. Accordingly, paper products coated with the above
described composition or indeed obtained according to the above
described method also form part of the present invention which will
now be described in more detail by way of the following
non-limiting examples.
EXAMPLES
Example 1
Comparison of the Properties of CMC and a Cold Water Swellable
(cws) Starch Ester According to the Invention
[0046] A series of tests with 0.2, 0.4 and 0.6 parts CMC FF5 (from
Noviant) were performed--parts expressed per 100 parts pigment. The
amount of Noresin.TM. A 180 (a cold water swellable starch
carbamate phosphate ester available from Blattmann Cerestar AG)
required, in each case, to reach the same Brookfield viscosity was
then determined.
CMC and Noresin.TM. Preparation:
[0047] CMC and Noresin.TM. were added to tap water at about
40.degree. C. and homogenised with a Type LD50 dissolver
(Pendraulik GmbH) for 30 minutes. The CMC was prepared at 15.1% dry
solids and the Noresin.TM. at 9.4% and 5.5% dry solids,
respectively. Brookfield viscosity was then determined at
50.degree. C. and 100 rpm (with a Brookfield RVF viscometer).
Results are shown in Table 1 and FIG. 4. TABLE-US-00001 TABLE 1
Viscosity data for: CMC Noresin .TM. Dry solids (%) 15.1 9.4 5.5 pH
5.4 7.2 7.2 Brookfield viscosity 100 rpm at 50.degree. C. 4050 9850
3120 (mPa s)
[0048] As can be seen from these results, CMC FF5, at 15.1% dry
solids (d.s.), has a Brookfield viscosity of 4050 mPas. Lab trials
showed that Noresin.TM., when used at 15% d.s., did not give
comparable results. Even a 9.4% solution of Noresin.TM. reached a
Brookfield viscosity of nearly 10 000 mPas and would therefore be
too viscous to handle. Accordingly, the appropriate dry solid
content of Noresin.TM. was determined to be 5-6% by weight (5,5%
reached 3120 mPas).
Coating Composition Preparation:
[0049] Coating compositions were prepared by mixing the ingredients
shown in Table 2 with the LD50 dissolver for 5-10 min. Dry
substance levels were adjusted by adding water at room
temperature.
Trials 1, 2, 3, 4a and 5a:
[0050] For these trials CMC and Noresin.TM. were added to the
pigment slurry before the latex binder was added.
Trials 4, 5 and 6-9:
[0051] For these trials, the latex binder was added first to the
pigment slurry, then Noresin.TM. was added.
[0052] For all trials, total dry solid content was adjusted to
approximately 69% by weight and the pH was adjusted to 8.5 by
addition of 50% NaOH solution.
[0053] The coating compositions were analysed according to standard
industry methods with regard to Brookfield viscosity (using a
Brookfield RVF viscometer) and Haake viscosity (Haake Rotovisco
RT20, rotor HS 25/stator HS 28, shear rate 45000 s.sup.-1). WRVs
(water retention values) were measured using the .ANG.bo Akademi
GWR method.
[0054] This analysis revealed that Noresin.TM. was much more
effective than CMC at lower addition rates. It was indeed found
that, to obtain a coating composition with a Brookfield viscosity
of approximately 500 mPas, the addition of 0.2 parts CMC was
comparable to the addition of only 0.05 parts of Noresin.TM.. To
reach a coating colour having a Brookfield viscosity of .about.1400
mPas only 0.35 parts Noresin.TM. were necessary compared to 0.6
parts of CMC. Accordingly, by using cold water swellable starch
esters instead of CMC, significant cost reductions can be made.
[0055] Best results (i.e. more moderate thickening) were obtained
with Noresin.TM. when it was added to the coating composition mix
after the latex binder. Thickening is further reduced by adding any
remaining water and fully homogenising the mixture.
[0056] The fall results of these trials are set out in Table 2 and
in FIGS. 1-6. TABLE-US-00002 TABLE 2 Trial no. ref. 1 2 3 4 4a 5 5a
6 7 8 9 Formulation (parts) Pigment Hydrocarb 60 (Omya) 100 100 100
100 100 100 100 100 100 100 100 100 Binder Baystal P 7110 (from
Bayer AG) 12 12 12 12 12 12 12 12 12 12 12 12 Thickener CMC FF 5
0.2 0.4 0.6 Noresin .TM. A 180 0.05 0.05 0.06 0.06 0.2 0.25 0.3
0.35 Coating composition data Total Dry solids 69.3 69.2 69.1 69.1
69.2 69 69 69 68.8 69 69.3 68.9 pH 8.5 8.5 8.5 8.5 8.5 8.6 8.5 8.5
8.5 8.5 8.5 8.5 Brookfield viscosity 100 rpm 256 525 950 1310 445
505 435 450 840 920 1130 1400 (mPa s) Haake viscosity 45000 1/s
10.2 12.6 16.5 22.6 -- 10.9 11.3 11.3 15 17.5 18.5 23.5 (mPa s) WRV
(g/m.sup.2) 360 285 253 231 -- 360 360 340 310 306 269 261
Example 2
Influence of Dry Solids on Brookfield Viscosity
[0057] A number of thickener solutions were prepared as detailed in
Table 3. Trials 1 and 1a used Noresin.TM. A 180. Trials 2 and 2a
used cold water swellable native maize starch (Cerestar). Trials 3
and 3a used oxidised cold water swellable starch (Cerestar). Trials
4, 4a, 4.1 and 4.1a used CMC FF150 (Noviant). Trials 5 and 5a used
a cold water swellable starch ether (Cerestar) and, finally, trial
6 used a cold water swellable hydroxypropylated, non-ionic potato
starch ether (Emsland Starke GmbH).
[0058] The thickener was added to tap water at 40.degree. C. in a 2
litre metal beaker and stirred at approximately 3200 rpm for 20
minutes. The amount of thickener added was calculated based on the
desired dry solid content (see Table 3). pH was adjusted to the
values shown in Table 3 using 50% NaOH solution (for each
thickener, a near-neutral and an alkaline pH were tested to emulate
the differences in viscosity and stability when these compounds are
used alone and in a coating composition). Brookfield viscosity,
Haake viscosity and water retention values (WRVs) were determined
using standard methods in the art (as above), both immediately
after preparation of the solutions and after overnight storage at
40.degree. C. The results are shown in Table 3 and in FIGS.
7-10.
[0059] It was found that Noresin.TM. produced stable viscosities at
varying pH and that, at 2.2% dry solids, Noresin.TM. produces a
Brookfield viscosity which can only be obtained with CMC, for
example, at 6% dry solids or with a cold water swellable starch
ether at 14.1% dry solids (see FIG. 7). It was also observed that
the Brookfield viscosity of Noresin.TM. solutions remains
surprisingly stable during storage, while the viscosity of
solutions prepared with cws native maize starch, for example, more
than doubles (see FIG. 8).
[0060] As shown in FIG. 9, the Haake viscosity of Noresin.TM.
solutions was desirably lower than that of solutions prepared with
alternative thickeners. Again, the Haake viscosity of Noresin.TM.
solutions was found to be stable during storage.
[0061] Water retention values of Noresin.TM. solutions were found
to be suitable for use in coating compositions and stable over time
(FIG. 10). In particular, it was found that the water retention
values of Noresin solutions were desirably lower than those of CMC
solutions at comparable dry substance. TABLE-US-00003 TABLE 3 Trial
1 1a 2 2a 3 3a 4 4a 4.1 4.1a 5 5a 6 Thickener (parts) Noresin .TM.
A 180 100 100 cws native maize starch 100 100 C*Plus 12015 cws
oxidised maize starch 100 100 C*Plus 12910 CMC FF150 100 100 100
100 cws maize starch ether 100 100 C*Film 12905 cws potato starch
ether 100 Emcol KP 190 Solution data dry solids 2.2 2.2 9.1 9.1
13.7 13.7 2.0 2.0 6.0 6.0 14.1 14.1 9.2 pH 7.5 9.5 7.9 9.5 7.9 9.5
7.7 9.4 6.6 9.6 7.6 9.5 10.7 Brookfield viscosity 980 1050 840 1080
1240 1060 153 149 1130 770 930 1100 750 100 rpm (mPa s) Haake
viscosity 45000 1/s 3.7 3.9 -- -- 28.5 28.4 7 6.7 36.1 34.8 49.6
50.2 57.7 (mPa s) WRV (g/m.sup.2) 328 325 110 111 100 115 >1000
>1000 333 400 279 275 448 Solution data after storage overnight
@ 40.degree. C., 50 rpm dry solids 2.2 2.2 9.1 9.1 13.7 13.7 2.1
2.1 6 6 14.2 14.2 9.4 pH 7.9 9.4 7.4 8.9 7.5 8.7 8.4 8.8 6.8 7.9
8.2 9.5 10.5 Brookfield viscosity 1120 1070 2640 2760 2200 1670
47.5 43.5 930 620 1800 1780 1080 100 rpm (mPa s) Haake viscosity
45000 1/s 4.5 4.5 -- -- 30.3 27.9 6.7 6.3 35.3 33 52.4 52.6 57.2
(mPa s) WRV (g/m.sup.2) 300 216 96 99 99 127 >1000 >1000 333
424 264 253 329
Example 3
Influence of Stirring Time on Brookfield Viscosity
[0062] Noresin.TM. and cws native maize starch solutions were
prepared by adding 2.3% dry substance and 8.9% dry substance,
respectively, to tap water at 40.degree. C. in a 1 litre metal
beaker. The solutions were then mixed at 3200 rpm for 20 minutes.
Brookfield viscosity was measured using standard methods (as
above). The results are set out in Table 4 and in FIG. 11.
TABLE-US-00004 TABLE 4 C*Plus 12015 Noresin .TM. (2.3% ds) (8.9%
ds) Time (min) Brookfield viscosity 100 rpm/30.degree. C. (mPa s) 5
1100 750 10 1040 680 15 1030 720 30 1010 880 60 950 1040 120 940
1170 180 930 1130 240 940 1210
[0063] As can bee seen from these results, the Brookfield viscosity
of Noresin.TM. solutions is surprisingly stable compared to that of
conventional thickeners.
Example 4
Influence of Thickener on Torque
[0064] Thickener solutions were prepared in 1 litre metal beakers.
The thickeners used and the dry solid content of each solution is
indicated in Table 5. The solutions were stirred (with an IKA
propeller stirrer, MR-AO.2) at 1500 rpm until a stable curve was
obtained. Torque was then measured (with a torque measurement unit
from IKA-Janke & Kunkel, RE-162) using standard methods.
Beginning and end values were recorded. The results are set out in
Table 5 and in FIG. 12.
[0065] It was found that Noresin.TM. at low dry substance (2% ds)
had similar torque values (i.e. shear resistance) to other
thickeners at much higher dry substance. When these more
conventional thickeners were used at low dry substance, it was
found that their torque values dropped substantially (in Table 5,
CMC is illustrated at 2% d.s.). TABLE-US-00005 TABLE 5 Noresin .TM.
C*Plus 12015 C*Plus 12910 CMC FF150 CMC FF150 C*Plus 12905 (2% ds)
(9% ds) (14% ds) (2% ds) (6% ds) (14% ds) Nm (beginning) 0.015 0.01
0.01 0.014 0.013 0.012 Nm (end) 0.038 0.046 0.042 0.018 0.038
0.042
Example 5
Influence of Dry Solids on Brookfield Viscosity
[0066] Solutions of thickener were prepared as described in Example
2. Brookfield viscosity (at 100 rpm and 30 .degree. C.) was
measured at several different dry solid contents for each
thickener. The results are set out in Table 6 and in FIG. 13.
TABLE-US-00006 TABLE 6 Noresin .TM. ds (%) 1.5 2.2 3.3 4.4 Brookf
(mPa s) 590 980 2280 4150 C*Plus 12015 ds (%) 8.6 9 10.2 Brookf
(mPa s) 800 1200 2260 C*Plus 12910 ds (%) 7.5 9 10.3 13.1 13.7 14.3
Brookf (mPa s) 122 194 290 620 1240 1680 CMC FF150 ds (%) 2 4 6
Brookf (mPa s) 50 250 1100 C*Film 12905 ds (%) 12.6 13.7 14.9
Brookf (mPa s) 550 735 1110 Emcol KP 190 ds (%) 5.2 6.5 9.2 Brookf
(mPa s) 260 400 750
[0067] These results confirm that high Brookfield viscosities can
be obtained with relatively low amounts of Noresin.TM. compared to
conventional thickeners.
* * * * *